The invention relates generally to temperature sensors and more particularly to a temperature sensor including a quartz oscillator for determining temperature by measuring the resonance or oscillation frequency of the quartz oscillator.
Examples of conventional quartz oscillators for determining temperatures are described in Japanese Patent Publication Nos. 61-29652 and 1-29089. These publications specify a wide range of orientations of the quartz wafer and quartz oscillators having a frequency-temperature characteristic with a large first-order coefficient. However, neither publication describes various characteristics which must be taken into account in order to fabricate suitable quartz oscillator temperature sensors so that reliable sensors can be fabricated with suitable consistency. Additional details regarding quartz oscillator temperature sensors are described in U.S. Pat. Nos. 5,265,316, 5,200,714 and 4,987,670, the contents of which are incorporated herein by reference.
The following characteristics affect the suitability of a quartz oscillator temperature sensor. The angular orientation of the oscillator can affect the equivalent series--resonance resistance value (CI value) of the oscillator. The quartz oscillator can have a large CI value, or it can have a large variation in CI value with change in temperature, depending on the particular angular orientation of the oscillator. If an oscillator is constructed with an improper angular orientation, oscillation stoppage can occur at high temperatures.
Another drawback can be the presence of fin shaped structures on the quartz tuning fork. Fins result from imprecise manufacturing techniques and can remain on the outer surface after the tuning fork is formed by a photo-etching method, for example. Fins can lead to unstable oscillation properties.
If a flexural oscillation mode is used that involves a high-order oscillation mode, many conventional quartz oscillators exhibit what is commonly referred to as "spurious" phenomena. Spurious phenomena is an abnormality in oscillation which occurs when the frequency coincides with an unnecessary oscillation mode at certain temperatures within the usable temperature range of the quartz oscillator. In order to detect spurious phenomena, the frequency-temperature characteristics of the oscillator must be checked precisely over the entire usable temperature range.
Accordingly, in order to overcome deficiencies in conventional quartz oscillator temperature measuring devices, it is necessary to provide a method and apparatus for eliminating deficiencies in equivalent series-resonance resistance caused by unsuitable angular orientation; unstable oscillation resulting from the presence of fins on the oscillator; and the existence of spurious phenomena. These and other drawbacks of conventional quartz oscillator temperature measuring apparatuses can be overcome by constructing a temperature measuring apparatus in accordance with the invention.